A sleep disturbance, in the form of repetitive, stereotypical anxiety dreams, occurs commonly in posttraumatic stress disorder (PTSD). In polysomnographic studies of PTSD, we have identified abnormalities of tonic and phasic rapid eye movement sleep (REMS) as a possible biological substrate. Two types of phasic events, rapid eye movement and leg muscle twitch bursts, occurred more frequently in PTSD subjects compared to controls. These two measures remained elevated on a subsequent recording night, suggesting that heightened REMS phasic event generation might be an essential property of sleep and the co-diagnosis of major depression found in many of the PTSD subjects. Distinguishing the REMS that may result from past alcoholism or primary major depression is the first objective of this proposal. The polysomnograms of a group of Vietnam combat veterans with PTSD and a control group, a matched subset of whom will have alcoholism, will be compared. In both groups, the potential influence of a diathesis for primary major depression will be minimized. We hypothesize that the PTSD subjects will show heightened REMS phasic activity compared to the controls.